CS4235 Datasheet, PDF (76/94 Pages) Cirrus Logic – CrystalClear Low Cost ISA Audio System

CS4235
CrystalClear ^TM Low Cost ISA Audio System
Miscellaneous Analog Signals
The VREF pin is typically 2.2 V and provides a
common mode signal for single-supply external
circuits. VREF only supports light DC loads and
should be buffered if AC loading is needed. For
typical use, a 0.1 µF in parallel with a 10 µF ca-
pacitor should be connected to VREF.
GROUNDING AND LAYOUT
Figure 22 is a suggested layout for motherboard
designs and Figure 23 is a suggested layout for
add-inn cards. For optimum noise performance,
the device should be located across a split ana-
log/digital ground plane. The digital ground
plane should extend across the ISA bus pins as
well as the internal digital interface pins.
DGND1 is ground for the data bus and should
be electrically connected to the digital ground
plane which will minimize the effects of the bus
interface due to transient currents during bus
switching. SGND1-4 should also be connected to
the digital ground plane to minimize coupling
into the analog section. Figure 24 shows the rec-
ommended positioning of the decoupling
capacitors. The capacitors must be on the same
layer as, and close to, the part. The vias shown
go through to the ground and power plane lay-
ers. Vias and power supply traces should be as
large as possible to minimize the impedance.
POWER SUPPLIES
The power supply providing analog power
should be as clean as possible to minimize cou-
pling into the analog section and degrading
analog performance.
The VD1 is isolated from the rest of the power
supply pins and provide digital power for the
asynchronous parallel ISA bus. The VD1 pin can
be connected directly to the system digital power
supply.
Digital
Ground
Crystal
Part
Noise
1
Analog
Ground
Digital
Ground
Digital Ground Noise
Digital ^{Ground Noise}
Power
Connector
Figure 22. Suggested Motherboard Layout
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DS252PP2